Callophrys rubi has a wingspan reaching about 26–30 millimetres (1.0–1.2 in).[3] The upperside of the wings is a uniform dull brown with two paler patches on the male's forewings made up of scent scales.[1] The undersides are a bright green with a thin white line, often reduced to a faint row of dots or even missing altogether. The iridescent green colour of the undersides is a structural colour caused by diffraction and interference of light by microscopic repeating structures in the wing scales.[4] The caterpillars are green with yellow markings along the back.[1] Like other members of the family they are rather sluglike.

These butterflies can be found already at the end of March, the flight time usually extend until the end of June, but sometime they were seen in July and early August.[3] They never rest with their wings open, in order to keep its green camouflage.[1][5] The males show a territorial behavior.[1]

The eggs are laid singly.[1] The caterpillars are not known to be tended by ants like some lycid larvae but the pupae, which are formed at ground level, emit squeaks which attract ants and it is thought that ants will always bury any that are found. Green hairstreaks overwinter as pupae and are univoltine, having one generation of adult butterflies per year.

This polyphagous species has what is probably one of the largest range of foodplants of any British butterfly. Early butterfly collectors thought that the only foodplant was Bramble (blackberry) Rubus fruticosus but as its habits became better understood the list grew and will probably continue to do so. Depending on the habitat it will use Common Rock RoseHelianthemum nummularium, Bird's-foot trefoilLotus corniculatus, GorseUlex europaeus, BroomCytisus scoparius, Dyer's GreenweedGenista tinctoria, BilberryVaccinium myrtillus, DogwoodCornus sanguinea, BuckthornRhamnus cathartica, Cross-leaved HeathErica tetralix and Bramble.[1]

The wide range of foodplants means that this butterfly is able to use a wide range of habitats including chalk downland, heathland, moorland and clearings in woodland.[1] It is present in wetlands as well as on poor dry meadows, at an elevation of about 0–2,300 metres (0–7,546 ft).[3][5]